Electric train signaling system



March 29, 1938. L. o. GRONDAHL 2,112,364

ELECTRIC TRAIN SIGNALING SYSTEM {Sheets-Sheet 1 Filed May 6, l93 0 M I 5 T/ I M Fi .5. i fllzerand Amplifier March 29, 1938. r L. o. GRONDAHL 2,112,364

ELECTRIC TRAIN SIGNALING SYSTEM 2 Sheets-Sheet 2 Filed May 6, 1930 Fill?! and Ampllfl'el; 1 7 s 12 %&-:VENEOR I Patented Mar. 29, 1938 2,112,364 anaemic ram SIGNALING SYSTEM Lars 0. Grondahl, Pittsburgh, Pa.,

Switch & Signal Company,

The Union assignor to Swissvale, Pa., a corporation of Pennsylvania Application May 6,

25 Claims.

My invention relates to communication systems for railway trains, and has for an object the provision of novel means for signaling between spaced points on a train, or between two trains,

'or between a train and a station along the track.

The present application is a continuation in art of my copending application, Serial No. 269,148, filed April 11, 1928, for Apparatus for sigtwo points on a railroad train.

I will describe several forins of apparatus embodying my invention, and will then point out the novel .features thereof in claims.

In the accompanying drawings, Fig. 1 is a diagrammatic view showing one way in which a railway train may be equipped with apparatus embodying my invention. Fig. 2 is a similar view showing another way in which a railway train may be equipped with apparatus embodying my invention. Fig. 3 is a detail view, partly diagrammatic, showing one unit of apparatus embodying my invention. Fig. 4 is a view simllar to Fig. 3 but showing a modified form of the unit illustrated in Fig. 3, and also embodying my invention. Fig. 5 is a diagrammatic view illustrating and returns in the body of the units illustrated in Fig. 3. Fig. 6 is a diagrammatic view showing two trains equipped with apparatus embodying my invention. Fig. '7 is a detail view showing a unit similar to the unit illustrated in Fig. 4, but having its inductor located in the trackway.

Similar reference characters refer to similar parts in each of the several views.

Referring first to Figs. 1 and 2, the reference characters'B and 9 designate the two forward vehicles of a railway train, and the reference characters Ill and H designate the two rear vehicles of such train. For example, the vehicles 8 and 9 may be the locomotive and tender of the train, the-vehicle It! may be a freight car, and the vehicle H may be a caboose. This particular make-up of train has no significance, however, in so far as my present invention is concerned. 8 and 9 are connected by the usual coupler 2, and the vehicles l and are likewise connected by similar means.

When my invention is to be utilized for signaling between spaced points on the same train, for example between the locomotive and the caboose, one unit of apparatus embodying my invention may be interposed between the vehicles 8 and 9 at the point A, and another unit embodying my invention may be interposed between ve- 1930, Serial No. 450,135

hicles l0 and H at point B. These particular locations are not essential, however; as shown in Fig. 2, one unit may be located on the vehicle 8 in advance of the forward axle of the train at the point C, and the other unit may be located on the vehicle H in rear of the rear axle of the train at the point D. Inasmuch as the caboose is likely to be operated in each direction, it may be preferable to provide this vehicle with two sets of inductors adjacent the two ends of the 10 vehicle, respectively.

When the forward unit is located in rear of the front axle of the train, and the rear unit is located forward of the rear axle of the train, as illustrated in Fig. 1, each unit will preferably be is constructed as shown in Fig. 3 As here shown, the reference characters 3 and 3 designate magnetizable cores which are mounted on one of the vehicles directly above the track rails l and I, respectively, and each of which cores is trans- 2 versely disposed with respect to the track rails.

A third core 4 is also mounted on one of the vehicles in close relation to the coupler 2, and is also disposed transversely with respect to the track rails. Cores 3 and 3 are provided with windings 5 and 5, respectively, and the core 4 The three wind- '6 and 6 are connected in series, and these windings may ator G of alternating curre t, or with a signaling device S, through a manually operable circuit controller 1. This circuit controller normally occupies the position in which it isshown in Fig.

.3, wherein the three windings are connected with the signaling device S through contact 1--I and a suitable filter and amplifier and, if necessary, a demodulator. When the circuit controller I is depressed, so that contact 'I---'I is closed, the three windings are disconnected from the signaling device S, and are connected with the gen- 40 erator G.

Each unit may also be provided with suitable means for modulating, at voice frequencies, the current winch is supplied to the windings 5, 5, and 6 when the switch I is depressed. As here shown, this means comprises a transformer T. the secondary l2 of which is interposed in the circuit over which current is supplied to the windings 5, '5 and 6 from generator G, and the primary l3 of which is connected with a microphone M through a battery l4.

The three windings 5, 5 and 6 are connected in series in such manner that when the circuit controller I is depressed, the currents which are induced in the body of the train and in the track rails at any instant all flow in the same direction. at point B, whereupon the signal device 8 on the The track rails and the body of the train in parallocomotive will respond. lei form a closed circuit which is completed The signal device 8 may be of any suitable through a common path including the track balcharacter, such as a loud speaker, bell, or lamp,

last resistance or rail-to-ground impedance and or any combination of these devices, depending 5 the ground. This is illustrated diagrammatically upon the kind of signals which it is desired to in Fig. 5. As here shown, the point at which curemploy. rent is induced in the rail i by the flux set up Each of the uni s i Preferably a ju d o imin the core 3 due to current in the winding 5'' is press substantially equal electromotive forces on indicated at P, and the approximate paths taken the two track rails I and I and on the coupler 2. 10 by this current are illustrated roughly by the The frequency f each g n ra or G may be any broken lines. l5. Similarly, the point at which suitable value, but is preferably high enough to current is induced in the body of the train is inavoid interference due to currents of commercial dicated at Q, and the approximate paths taken or other frequencies. Each filter is, 1' c r by this current are indicated roughly by the tuned to transmit the frequency of the generator 15 dotted lines l8. It shouldbe distinctly under- G and to block all other frequencies. stood, however, that this illustration is provided When a unit is mounted in front of the forward merely for the purpose of indicating that the axle of the train or in rear of the rear axle of induced currents flow in a closed circuit includh tra n. as i ra in i Wh n the 2 ing the track rails, the body of the train, rail-toconductivity of the path through the vehicles and ground impedance and the ground, and not for the couplers is comparatively high, the core 4 ually diminishes as the distance from the points lustmted n i AS here w the uni i 2 the broken lines [5 f rm l d loops h of and inI inductive relation with, both track rails 30 to some point on one side of the point P, then In Order to 8 1 w n wo r in ch 0! through the ballast leakage resistance and the the trams m y e p ovided with one or more units 5 side of the point P, and hence through the rails the trains example, as Shown n each rails flows in opposite directions through two sides train is depressed, the r l n current which 40 the cur ent induced in th rails and m m body tween the locomotive 8 andtender 9' of this 45 curr nt are additive, and the resultant current When it is desired to signal between a train and 50 i amplified t operate signal s a station along the track, the train may be The operation of the apparatus is as follows: equipped with one or more units in the n r Normally the circuit controller 1 is in such posi- Previously described, and another unit or units m t t Contact 1 1a is closed, so that the maybe located at some convenient point or points naling device S of each unit is connected with ,along the track- The unit which is located long 55 associated generator G with the inductor winch unit instead of being located on a train above the 60 track rails and the body of the train in the manggg g g g readily understood without further 65 It might appear that the operation of apparatus embodying my invention would be interfered signaling system. I have found, however, that 70 occupant of the caboose may communicate with herent capacity between the rails at the joints, the engineer by depressing the key 1 of the unit or both, and that, consequently, the joints will 75 not prevent correct operation of the apparatus. Furthermore, if it is found in some instances that such joints do interfere with the transmission of signal indications from one end of the train to the other, the difficulty may be removed by bridging each insulated joint by a condenser adjusted to conduct the relatively high frequency train signal current but not the current used for the track circuits of the block signal system.

Although I have herein shown and described only a few forms of signaling systems for railway trains embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a railway train, means located on one vehicle of the train for inducing alternating currents in the body oi the train and in the track rails in such manner that the currents flow away from the points at which they are induced in the same direction at any instant and return to the points at which they are induced partly through the ground, and means located on another vehicle of the train and controlled by the currents in the train body and in the track rails due to said first mentioned means.

2. In combination, a railway train, means located on one vehicle oiE-the train for inducing in the body of the train and in the track rails alternating currents which at any instant flow away .from the point at which they are induced in the same direction and return to the point at which they are induced partly through the ground, means located on another vehicle of the train for inductively receiving a voltage due to said currents in the train body and track rails, means for amplifying said received voltage, and a signaling device actuated by the output of said amplifying means.

3. In a communication system for railway trains, transmitting means located at one point on a train for simultaneously inducing modulated alternating currents in each track rail and in the body of the train all of which currents flow-in.

the same direction at a given instant and return to the points at which they are through the ground, and signaling means located at another point on the train and responsive to the modulated alternating currents flowing in the train body and track rails due to said transmitting means.

4. Apparatus for signaling between two points on a railway train, comprising three windings located at one point on the train and disposed in inductive relation to the two track rails and a coupler respectively, three windings located at another point on the train and disposed in inductive relation to the two track rails and a coupler respectively, of alternating current and a receiving points, and manually operable means at each said point for connecting the three said windings with either said source or said receiving device at the same point.

5. Apparatus for signaling between two points on a railway train comprising three windings located at one point on a train and disposed in inductive relation to the two track rails and a coupler respectively, three windings located at another point on the train and disposed in inductive relation to the two track rails and a coupler respectively, means at one of said points induced partly for supplying alternating current to the three said windings in such manner that the currents induced thereby in the track rails and train body all flow in the same direction'at any given instant, a receiving circuit located at the other point and including the three said such manner that the currents induced therein by the currents in the track rails and train body all flow in the same direction at any given instant, and signaling means controlled by the current in said receiving circuit. I

6. Apparatus for signaling between two points on a railway train, comprising three windings located at one point on the train and disposed in inductive relation to the two coupler respectively, three windings located at another point on the train and disposed. in inductive relation to the two track rails and a coupler respectively, means at one of said points for supplying alternating current to the three said windings in such manner that the currents induced thereby in the track rails and train body all flow in the same direction at any given instant, a receiving circuit ,located at the other point and including the three said windings connected in such manner that the currents induced therein by the currents in the track rails and train body all flow in the same direction at any given instant, filteringiand amplifying means.-

connected with said receiving circuit, and. signaling means operated by the output of said filtering and amplifying means.

7. Apparatus for signaling between two points on a railway train, comprising three windings located at onepoint on the train and disposed in inductive relation to the two track rails and a coupler respectively, three windings located at another point on the train and disposed in inducto the two track rails and a coupler respectively, a source of alternating current and a receiving device associated with each said group of windings, manually operable means at each said point for at times connecting the associated source with the three associated windings in such'manner that the currents induced thereby in the track rails and train body all flow in the same direction at any given instant and for at other times connecting the three windings with the associated receiving device in such manner that the currents induced in the windings are additive.

8. Apparatus for signaling between two points on a railway train, comprising three windings located at one point on the train and disposed in inductive relation to the twotrack rails and a coupler respectively, three windings located at another point on the train and disposed in inductive relation to the two track rails and a coupler respectively, and a receiving device associated with each said group of windings, manually operable means at each said point for at times connecting the associated source with the three associated windings in such manner that the currents induced thereby in the track rails and train body all flow in the same direction at any given instant and for at other times connecting the three windings with the associated receiving device in such manner that the currents induced in the windings are additive, and filtering and amplifying means interposed between said windings and said rewindings connected in alternating current to the two track rails and a coupler respectively, three windings located at another point on the train and disposed in inductive relation to the two track rails and a coupler respectively, a, source of high frequency alternating current at one of said points, a circuit at said one point including said source and the three associated windings connected in series in such manner that the currents induced in the track rails and train body by current supplied to the windings over said circuit all flow in the same direction at any given instant, means included in said circuit for modulating the current supplied to the associated windings from said source at voice frequencies, a receiving circuit located at the other point and including the three windings at said other point connected in suchmanner that the currents induced therein by the currents in the track rails and train body all flow in the same direction at any given instant; filtering, demodulating, and amplifying means connected with said receiving circuit; and signaling means operated by said filtering, demodulating, and amplifying means.

10. In combination, a railway train, means located on the train for inducing in the track rails alternating current which flows in a closed circuit including the rails, the distributed rail-toground impedance and the ground, and means located in the trackway and controlled by the currents flowing in the track rails due to said first mentioned means.

11. In combination, a railway train, means located on one vehicleof the train for inducing in the track rails alternating current which flows in a closed circuit consisting of the rails, the distributed rail-to-ground impedance and the ground, and means located on another vehicle of the train and controlled by the current flowing in the track rails due to said first mentioned means.

12. In a, signaling system for railway trains;

a circuit consisting of the track rails, the distributed rail-to-ground impedance and the ground as a conducting path; a train, transmitting means located along the track for causing a periodic signaling current to flow in said circuit, and receiving means located on a vehicle of the train effectively influenced by such current flowing in said circuit due to said transmitting means.

13. In a signaling system for railway trains; a circuit consisting of the track rails, the distributed leakage conductance of rail to ground and the ground as a, conducting path; a train, transmitting means located on a vehicle of the train for causing a periodic signaling current to flow in said circuit, and receiving means located along the trackway effectively influenced by such current flowing in said circuit due to said transmitting means.

14. In a signaling system for railway trains, a train, transmitting means on a vehicle of the train for causing periodic signaling current of effective magnitude to flow in a portion of a track rail both in advance of and to the rear of said vehicle by virtue of a path completed through the rail and the ground and the distributed rail-toground impedance, and receiving means effectively influenced by current flowing in said portion of track rail due to said transmitting means.

15. In a signaling system for railway trains, a train; a circuit consisting of the track rails, the rail-to-ground impedance and the ground as the conducting elements; transmitting apparatus mounted on one vehicle ofthe train and coupled with the track rails to cause a. signaling current to flow in said circuit for establishing an effective zone or influence which extends in both directions from said vehicle and moves with the vehicle, and receiving apparatus mounted on another vehicle of the train spaced within such zone and coupled with the track rails for receiving current in response to the current flowing in said circuit due to said transmitting apparatus.

16. In a signaling system for railway trains. a train, a traveling circuit associated with. 8. vehicle of the train; said circuit consisting of a section of the track rails on which an electromotive force is impressed, the track rails extending in both directions from. the vehicle, the railto-ground impedance and the ground as a conducting path; transmitting apparatus mounted on said vehicle and coupled with the track rails for producing the electromotive force insaid circuit, receiving apparatus mounted on another vehicle of the train and coupled with the track rails for receiving an electromotive force in response to the current flowing in said circuit due to the electromotive force produced by said tran'smitting apparatus, and signaling devices eifec-' tively lnfluencedlby such received electromotive force.

1'7. In a signaling system for railway trains, a train; transmitting apparatus located on one vehicle of the train and coupled the track in both directions from said which moves with the vehicle,

and to the distributed receiving apparatus and coupled with the track rail along said portion of the track rail for eifectively influencing said device in response to the current flowing in the rail due to said transmitting apparatus.

19. In a signaling system for railway trains, a train; a circuit consisting of the track rails, the rail-to-ground impedance and the ground as the conducting elements; transmitting apparatus and receiving apparatus mounted on eachof two vehicles of the train, said transmitting apparatuses each including a source of periodic signaling current to cause such current to flow in said circuit for establishing an effective zone of inextending in both directions from the point at which such electromotive force is produced, and receiving apparatus including means coupled with the rails within such distance effectively influenced by such current of said given magnitude. 23. In a signaling system for railway trains, a train; transmitting apparatus mounted on one vehicle of the train including a generator of carrier current, a signaling transmitter for modulating the carrier with a predetermined frequency and means for delivering the'carrier signaling current to the track rails; receiving apparatus mounted on another vehicle of the train responsive to such signaling current and including means for receiving current from the track rails, said generator proportioned to generate a carrier frequency that is high enough that interference from commercial power frequencies is substantially avoided but which is sufficiently low to be substantially free from electromagnetic wave radiation and for which frequency the rail impedance is sufiiciently low that said transmitting apparatus is efiective to cause current of a given magnitude to advance of and to the rear of said one vehicle for a distance of. the order of magnitude of one mile by virtue of the rail-to-ground leakage conductance and the ground as a conducting path, and said receiving apparatus provided with an amplifier so as to be effectively influenced by current of said given magnitude. 24. In a signaling system for railway trains, transmitting apparatus on one vehicle of a train, including a conductor coupled with one, at least, of the usual track rails of the track to produce an electromotive force in the rail for causing a periodic difference of potential between points in the rail in advance of and to the rear of said vehicle, and receiving apparatus on another vehicle of the train including an amplifier and a conductor coupled with said rail, said track rail where extending beyond said one vehicle constituting. an indefinitely extended open end conductor with a maintained though gradually diminishing difference of potential to cause distributed ground currents to flow through the leakage conductance, a fraction of which current affects the conductor of said receiving apparatus. 25. In a signaling system for railway trains, transmitting apparatus on one vehicle of a train including a source of periodic signaling current, receiving apparatus on another vehicle of the train including an amplifier, an open metallic circuit including a track rail as a conductor extending along the right-of-way and disposed for relatively low leakage conductance which is substantially uniformly distributed throughout the length of the track rail, means to couple said transmitting apparatus to said track rail to set up an electromotive force in said track rail for producing a current in the track rail by virtue of said distributed leakage conductance, said current gradually diminishing in magnitude as the distance is increased from the point where the electromotive force is set up, and means to couple the receiving apparatus to said track rail for impressing on the amplifier of said receiving apparatus an uted current to ground which flows in the track rail beyond the inter-vehicle sectionat the receiving end and returns beyond such section at the transmitting end.

fluence which extends in both directions from the associated vehicle, said two zones thus established overlapping and moving with the train, said receiving apparatuses each including a signaling device responsive to such current flowing in said circuit due to the transmitting apparatus of the other vehicle, and means on each of said vehicles for selectively governing its apparatuses to effect two-way signaling between said vehicles by virtue of said circuit.

20. In a signaling system for railway trains, a train, stretch of track which is divided for wayside signaling purposes into sections by insulated rail joints, transmitting apparatus located on one vehicle of the train and including a source of periodic communication current, means to couple the transmitting apparatus with the track rails to cause such communication current to flow in the track rails both in advance of and to .the rear of said vehicle by virtue of the distributed rail-to-ground impedance, and to flow around an insulated joint by virtue of the capacitance and the leakage conductance between the rail sections near the insulated joint, receiving apparatus located on another vehicle of the train and including a device responsive to such communication current, and means to couple said receiving apparatus with the track rails for efiectively influencing said device in response to current flowing in the rails due to said transmitting apparatus.

21. In a signaling system for railway trains, a train; transmitting apparatus mounted on one vehicle of the train includinga generator of carrier current, a telephone transmitter for modulating the carrier with voice frequencies and means for delivering the carrier telephone current to the track rails; receiving apparatus mounted on another vehicle of the train responsive to such telephone current and including means for receiving current from the track rails, said generator proportioned to generate a carrier frequency which is above the highest voice frequency to be transmitted so that interference from commercial power frequencies is reduced but which is sufficiently low to be substantially free from electromagnetic wave radiation and for which frequency the rail impedance is suificiently low that said transmitting apparatus is effective to cause current of a given :magnitude to flow in the rails both inadvance of and to the rear of said one vehicle for approximately a freight train length by virtue of the rail-toground leakage conductance and the ground as a conducting path, and said receiving apparatus proportioned to be effectively influenced by such current of said given magnitude.

22. In a signaling system for railway trains; a circuit consisting of the track rails, the rail-toground leakage conductance and the ground; transmitting apparatus mounted on the train including a generator of carrier current, a telephone transmitter for modulating the carrier with voice frequencies and means for producing in the rails an electromotive force corresponding to such modulated carrier; said generator being proportioned to deliver a carrier of a frequency outside of the radio communication band and for which frequency the rail inductancebears such a relation to the leakage conductance to ground thatsaid electromotive force is effective by virtue of said circuit to cause current of a given magnitude to flow in the rails for a dis- LARS O. GRONDAHL.

tance of the order of magnitude of one mile flow in the rails both in electromotive force due to distrlb- 

